Variable rate electrohydraulic actuator systems,particularly for ship&#39;s steering and/or propeller pitch control



United States Patent [72] Inventors Peder K. Wennberg 3,404,856 /1968Gerstine 244/77 Sands Point, New York; 3,447,783 6/ 1969 Wijkander 170/160.32 Ut'fe Hornsyld, Huntington, New York; Francis West, Jr., Seaclin, New York 2123 g fiz [21] Appl. No. 737,224 y [22] Filed June 14,1968 [45] Patented Sept. 8, 1970 ABSTRACT: A variable rateelectrohydraulic actuator system Asslgnee Pl91311151011 systems, Inc.drives a ships hydraulic steering motor and/or propeller pitchPl"wfl5hill81n,NeW York control motor at variable rates. Magneticamplifiers of dif col110mmm ferent output sensitivities have theirinputs connected preferably in series with the command signal source butrespond selectively thereto, such that each amplifier and its [541VARIABLE RATE ELECTROHYDRAULIC associated relay will cut in anassociated constant delivery ACTUATOR SYSTEMS PARTCULARLY FOR pump so asto drive the hydraulic motor at the rate indicated SHIPS STEERING AND/0RPROPELLER PITCH by the command signal. The amplifiers are arranged in aDC. CONTROL bridge c|rcu|t formed by command and feedback potentiome- 22Chums, 6 Drawing Figs ters. 1n the pitchchanging system, the bridgefurther inciudes a rheostat WhlCh set by a propulsion engine governor soas to [52] US. Cl 114/144 be indicative of the load condition on theengine Under oven [51] /00 load conditions, the rheostat biasses thecircuit in a pitch Field of Search 114/150; reducing sense Theelectrical cation of the rheostat in the 170/ 160.32; 91/459; /525circuit is automatically changed upon going from forward to asternpitch, or vice versa. A single command lever is opera- [56] Referencescued tive to drive programmed cams which vary both engine speed UMTEDSTATES PATENTS and propeller pitch in accordance with a predeterminedpro- 2,4l9,812 4/1947 Bedford 318120.430 gram. Especially in the pitchchanging system, the distributor 2,940,263 6/ 1960 Cudnohufsky 91/459Xvalve for the hydraulic motor comprises a servo valve which is 3,154,92111/1964 Junck et al 60/52 hydraulically stroked by a pilot valve, andthe spool of the 3,216,331 1 l 1965 Kreuter 9 11459 servo valve isconnected to the ported sleeve of the pilot valve 3,242,407 3/1966Hansen 318/20.430X f so as to ensure precise followup.

MAGNETIC DIFE MA TI AMPLIFIER RELAY AMSEIEFIECR :EIEZY r I .0 l 1 2| IPatented Sept. 8, 1970 3,527,186

AI C

DIFE

MAGNETIC AMPLIFIER RELAY DIFF RELAY MAGNETIC AMPLIFIER INVENTORS PEDERK. WENNBERG UFFE HORNSYLD FRANCIS WEST,JR.

BY D y/w ATTORNEYS Patented Sept. 8, 1970 Sheet v INVENTORS PEDER K.WENNBERG UFFE HORNSYLD FRANCIS WEST,JR. 3

agw ATT RNEYS BY J? Patented Sept. '8, 1976 Sheet \o ww W vw 8 9 av ZW Dg/9r ATT RNEYS Patented Sept- 8, 1970 3,527,186

Sheet 5 of 5 INVENTORS PEDER K WENNBERG UFFE HORNSYLD FRANCIS WEST,JR.

L I m 8 J cseg g ya ATTORN E Y8 VARIABLE RATE ELECTROHYDRAULIC ACTUATORSYSTEMS, PARTICULARLY FOR SHIPS STEERING AND/OR PROPELLER PITCH CONTROLFIELD OF THE INVENTION This invention relates to electrohydrauliccontrol systems, especially steering systems and propeller pitch controlsystems for marine vessels. More particularly, the invention relates todual rate or variable rate electrohydraulic actuator systems forcontrolling the steering motors or the propeller pitch changing motorsof such vessels.

BACKGROUND AND SUMMARY OF THE INVENTION There are many instances where ahydraulic motor must be driven at variable rates but with precisecontrol. There are many ways of achieving variable rate motor operation,for example, by using variable delivery pumps. It is an object of thisinvention to achieve variable rate operation through an improved systemwhich can use inexpensive constant delivery pumps by rendering themselectively responsive to the same source of variable command signals insuch a way as to obtain variable but precise operation of the motor.

In order to utilize the many advantages of a controllable pitchpropeller, the control system must be capable of extremely precise pitchpositioning, as well as very rapid pitch changes to facilitate vesselmaneuvering. It should also be capable of reducing the pitchautomatically to relieve propulsion engine overload while maintainingengine speed, and to provide an exact program of engine speed versuspitch angle from full ahead to full astern. High accuracy in pitchpositioning is required, as a small change in pitch represents arelatively large change in engine power demand, especially through thehigh ranges of pitch and speed. It is an object of this invention toprovide a control system which embodies all of these capabilities andadvantages.

As in the controllable pitch propeller system, the steering controlsystem of a vessel must be capable of extremely precise rudderpositioning, as well as very rapid rudder changes to facilitate vesselmaneuvering. There is little if any difficulty in providing a systemwhich adequately satisfies one of these requirements, but since rapidityand preciseness are basically conflicting requirements, many controlsystems achieve one characteristic at the expense of the other. It is ageneral object of this invention to provide a variable speed ruddercontrol system which fully achieves simultaneously the capabilities ofrapidity and preciseness.

In accordance with the invention, as applied to a hydraulic steeringmotor or to a hydraulic pitch control motor, an actuator system isprovided which achieves variable rate control with a combination ofrelatively inexpensive constant delivery pumps which are arranged torespond selectively to common command signals. In the preferredarrangement, this is achieved by subjecting to the same command signalat least two pump controlling amplifier systems of different outputsensitivities so as to be selectively responsive to signals of differentmagnitudes. Preferably a low volume pump starts and stops the motormovement, thus allowing very precise positioning of the motor, while ahigh volume pump is cut in at the proper time to allow rapid movement ofthe motor. To avoid or at least minimize synchronization difficulties,the pump controlling amplifiers in a system are located in circuit witha single command signal source, such as bridge connected command andfeedback otentiometers. To further minimize or avoid synchronizationdifficulties, and to improve control over the exact cut-in and cut-outtiming of the high volume pump, the amplifiers are connected with theirinputs in series so that each will always be subjected to the samecommand signal as the other. The amplifiers control relays which in turncontrol the pump valves for bypassing the pump outputs or directing theoutputs to the motor. One of the relays, in a known manner, is adifferential relay which actuates a selector valve for directing thepump output or outputs to the proper side of the motor so as to drivethe motor in the commanded direction as well as at the commanded rate.In the preferred embodiment, the output of the high volume constantdelivery pump is directed to the motor when the net command signalexceeds a predetermined value, for instance, a value indica tive of adifference of 5 or more between actual motor position and commandedmotor'position.

In the propeller pitch control embodiment of the invention, therepreferably is included an engine overload protective arrangement. In itspreferred form, this protective arrangement comprises a rheostat whichis controlled by an engine load sensing governor such that the settingof the rheostat is indicative of the load condition of the propulsionengine, and hence is indicative of an overload condition when apredetermined rheostat setting occurs. As mentioned above, the commandand feedback potentiometers and the amplifiers are connected in a bridgecircuit, and the overload rheostat is connected in the bridge so as tobias the bridge circuit in a pitch reducing sense in response to anoverload condition of the engine. To render this protective featureoperative during both astern and ahead pitch conditions, a relayautomatically functions to connect the rheostat in the proper electricallocation for the particular pitch condition. For instance, by connectingthe rheostat in series with one side of the command potentiometer, itwill be effective to reduce pitch to relieve engine overload during, forinstance, ahead pitch conditions. To render it effective during asternpitch conditions, the relay automatically responds to movement of thecommand lever to connect the rheostat on the other side of the commandpotentiometer.

Also in the pitch controlling embodiment of the invention, the pitchcommand potentiometer preferably is driven through a cam arrangementwhich in turn is controlled by the command lever. In addition to thepitch cam and a cam for operating the relay to shift the electricallocation of the overload rheostat, the command lever preferably drives afurther cam arrangement which controls the engine speed. The variouscams are designed so as to control the pitch and the speed in aprogrammed manner and hence the speed and the pitch are always varied inaccordance with the program, except when the overload rheostat biassesthe control circuit to reduce the pitch so as to relieve engine.overload. The single lever control and the programmed relationshipbetween pitch and speed greatly simplify the control of the vessel.

In either embodiment of the invention,'the directional valve fordirecting the pump output or outputs to the proper side of the motor mayadvantageously be an improved compound valve consisting of a servo valvewhich is hydraulically stroked by a pilot valve, the pilot valve in turnbeing stroked by a servo motor of the command system. In the preferredform of the valve, the pilot valve has a ported internal sleeve which isconnected to the spool of the servo valve for followup, so that theservo valve spool follows exactly any movement of the pilot valve spool.

In accordance with the foregoing, it will be apparent that it is ageneral object of this invention to provide a variable rateelectrohydraulic actuator system, particularly for ships steering and/orpropeller pitch control systems, and that more particular objects ofthis invention reside in the provision of improved such systemsincorporating one or more of the foregoing additional features,capabilities and advantages. Other and further objects, advantages andfeatures of the invention will be apparent to those skilled in the artfrom the ensuing description of exemplary preferred embodiments and thecorresponding illustrations set forth in the accompanying drawings.

We have set forth with particularity and distinctness in the appendedclaims those features which we consider to be characteristic of ourinvention, but the invention itself, its construction and arrangement,as well as the manner of use and operation thereof, will be bestunderstood from the exemplary descriptions and illustrations to follow.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic diagram of avariable rate steering control system in accordance with the invention.

FIG. 2 is a schematic diagram of a modification of the system of FIG. 1,only the modified portion and the immediately surrounding portions beingshown, since the system of FIG. 2 is otherwise identical to the systemof FIG. 1.

FIGS. 3A and 33 together constitute a schematic diagram of a variablerate propeller pitch control system in accordance with the invention,some components of the system being shown in each figure so as tofacilitate interrelating the two figures.

FIG. 4 is a graphic illustration of the relationships between propellerpitch setting and engine speed over the full range of positions of thecontrol handle or lever in the system of FIGS. 3A and 3B.

FIG. 5 is a cross section illustrating the basic features of theimproved directional valve which is shown schematically in FIG. 3A, andwhich preferably is used in the system of FIGS. 3A and 3B.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to FIG. 1, a shipssteering wheel 1 is drivingly coupled to command potentiometer 2. Theships rudder 13 is driven by hydraulic rudder actuator 12, and isdrivingly coupled as shown schematically at 14 to feedback potentiometer15. Command potentiometer 2 and feedback potentiometer are connected ina conventional manner to form a DC. wheatstone bridge circuit (e.g., seeUS. Pat. No. 2,812,026). A variable resistor 3 is connected in the pathof the D.C. signal so as to control the overall sensitivity of the servoloop. Also connected in the D.C. signal path is the control winding ofpush-pull magnetic amplifier 4, as is the control winding of identicalmagnetic amplifier 6. Magnetic amplifier 6, however, has a variableresistor 6a connected in the output of the amplifier so that a highersignal level is required to close its relay contacts 7 than is requiredto close one of the contacts of differential relay 5 of magneticamplifier 4. Differential relay 5 controls solenoid coils 9 and 10 ofhydraulic directional valve 8, while relay 7 controls the solenoid coilof cut-off valve 16, which in turn controls relief valve 17.

Electric motor 18 drives constant delivery pumps 19 and 20, pump 20preferably being a high volume, constant delivery pump, while pump 19 isa lower volume, constant delivery pump. The pump outlets are connectedto directional valve 8 downstream of one-way valves 21 and 22 as shown,and are also connected to relief valve 23. Additionally, valve 17 isconnected to serve as a bypass valve for high volume pump 20.Directional valve 8, of course, directs the pump output or out puts toone side or the other of hydraulic motor or actuator 12 when solenoidcoils 9 or 10 are energized, or moves to a third or normal position inwhich it disconnects the pump output from actuator 12. The fluid linesrunning from directional valve 8 to actuator 12 include relief valves 11as shown.

In the operation of the system shown in FIG. 1, movement of steeringwheel I causes a corresponding deflection of command potentiometer 2.The D.C. signal thus established is impressed on the control windings ofmagnetic amplifiers 4 and 6. The output of amplifier 4 will cause one ofits relay contacts to close in response to the signal. The polarity ofthe input signal determines which relay contact will close, andconsequently which solenoid coil of hydraulic directional valve 8 willbe energized. Oil from the directional valve is directed to the rudderactuator 12, causing rudder movement, port or starboard, depending onthe polarity of the potentiometer input signal. Followup potentiometer15, linked to the rudder, develops an opposing signal to stop the ruddermovement at a position depending on the magnitude of the command signal.

Due to the variable resistor 6a imposed in the output of amplifier 6, ahigher signal level is required to close relay 7 and to energize thesolenoid of the cut-off valve 16. In the unenergized condition, valve 16is open, causing relief valve 17 to be vented, which in turn causes theoutput of high volume, constant delivery pump 20 to be bypassed to thesump tank. When the solenoid is energized, valve 16 is closed and reliefvalve 17 then becomes operative, thus causing the output of pump 20 tocombine with the output of the low volume, constant delivery pump 19 fora high rate of rudder movement. With pump 20 bypassed, the rudder movesat a low rate, which allows the rudder to be positioned with highaccuracy or to be moved in very small increments.

For rudder orders of small magnitude, the relay contacts 7 of amplifier6 will not close, as relatively high signal levels are required. Butwhen the rudder command leads the actual rudder angle by 5 or more,amplifier 6 operates, and the rudder starts to move at a high rate asdescribed above. As the rudder approaches its ordered position, thesignal level drops enough to open contacts 7 of amplifier 6, thusslowing the rudder to its low rate, at approximately 3 before the finalposition of rest. Resistor 6a may be varied to adjust the cut-in andcut-out timing of high volume pump 20 to suit any operating conditions.Since both amplifiers are responding to the same signal, their outputsare inherently synchronized, and hence the timing adjustment is a simpleprocedure.

Referring now to FIG. 2, the system of FIG. 2 is basically a simplifiedversion of the system of FIG. 1. The corresponding parts and componentsin FIG. 2 are designated by primed reference characters corresponding tothose of FIG. 1. Basically the system of FIG. 2 differs from that ofFIG. 1 in using one amplifier instead of two. Thus amplifier 4' drivestwo relay coils in parallel, the extra relay coil being indicated at 6'in association with relay contacts 7'. Relay coil 6 is in series withvariable resistor 60, and hence requires a higher level of input signalbefore it will close relay contacts 7. Operation of the system isidentical to that shown in FIG. Lexcept that amplifier 4' must have ahigher gain to operate two relay coils at the same relative input signallevel. Although the system of- FIG. 2 is a simpler embodiment oftheinvention, the system of FIG. 1 is at present considered to constitutethe preferred embodiment or best mode of carrying out the invention asapplied to a steering control system.

Referring now to the pitch control system shown in FIGS. 3A and 3B, thecontrollable pitch propeller is ofa known type, and consists of hub 28,rotatable blades 26, pitch changing piston 24, crank pin 27, and slideyoke 27a. Propeller shaft 29 is hollow, and carries piston rod 25. Thepiston rod is provided with oil passages 30 and 31 to operate the piston24, and extends through the gear reduction unit 32 to a differentiallever 47 to obtain exact pitch position for servo followup. Low volume,constant delivery pump 34 and high volume, constant delivery pump 33 aredriven by motor 35, and, as in the preceding steering system embodiment,have their outlets connected to a hydraulic directional valve indicatedat 44. One-way valves 36 and 37, unloading relief valves 41, systemrelief valve 38 and solenoid controlled cut-off valve 42 are connectedas in the steering system embodiment. Additionally, power fluid istapped off at 40 and passes through reducing valve 39 to a pilot valve43 which controls or hydraulically strokes servo directional valve 44.The spool of servo valve 44 is connected as schematically indicated at45 to a ported sleeve surrounding the spool of pilot valve 43, as willbe explained in greater detail in connection with FIG. 5. Pilot valve 43is stroked or actuated by servo motor 51 which is drivingly coupled togear member 50, which in turn is connected to differential lever 47through a rod 48, the spool of pilot valve 43 being connected to thedifferential lever by rod 46. The differential lever is pivotallyconnected in a known manner at 49 to piston rod 25.

Servo motor 51 is controlled in a known manner by magnetic amplifier 60and its differential relay 61 so as to stroke the pilot valveappropriately. Magnetic amplifier 60 is connected in a D.C. bridgecircuit, two arms of which are formed by command potentimeter 53, andthe other two arms of which are formed by feedback or followuppotentiometer 52.

Also includedin the bridge circuit is magnetic amplifier 59 with itsrelay contact 62. As in the preceding embodiment. magnetic amplifier 59is arranged so as to close relay contact 62 only in response to apredetermined signal level greater than the signal level at whichamplifier 60 closes relay contacts 61. and only when pitch command leadsthe actual pitch by This conveniently can be accomplished by suitableamplifier gain adjustment 59a. Relay contact 62 controls solenoid valve42. which in turn controls relief or unloading valve 41,.in the samemanner as in the preceding steering system embodiment. Variable resistor58is incorporated in the bridge and controls the overall sensitivity ofthe servo loop.

Command potentiometer 53 is deflected in one direction or the other bycontrol handle or lever 54 through a cam schematically indicated at 55and a connection shown schematically at 57. To permit simultaneouscontrol of propeller pitch and engine speed by control lever 54. thelever is also drivingly coupled to cam 69a. which actuates speed commandpotentiometer 68 through a follower connection indicated schematicallyat 69. The electric speed control signal developed by potentiometer 68is impressed. as indicated schematically at 70. on engine governor 67 ofa well known design. in order to maintain engine speed at the orderedlevel. As will be discussed in more detail subsequently. governor 67 isalso capable of measuring engine overload. and of rotating a rheo stat66 in proportion to the magnitude of the overload.

By appropriate shaping of earns 55 and 69a. simultaneous programmedcontrol of propeller pitch and engine speed by single control lever 54is readily achieved. Such shaping is well within the skill of the art.given the desired operation. and accordingly the actual profiles are notshown in the drawings.

A typical program of engine speed versus propeller pitch is illustratedin FIG. 4. ln accordance with this program. movement of the controlhandle from its center position to full ahead would increase ahead pitchto full angle while maintaining the engine at idle speed. and thenincrease engine speed to full speed. or to a lower desired speed. Theastern program is similar. except that astern pitch is normally limitedto 80 percent ofahead pitch.

The operation of the basic system of FIG. 3Aand 38. as described thusfar. will be readily apparent. Thus. when control handle 54 is moved toa desired position. cams 55 and 69a are rotated accordingly. and startthe program of pitch and speed change. (am 690 moves the tap of speedcommand potentiometer 68. and the resulting electrical signal isimpressed on engine governor 67 to effect the speed change.

Rotation of cam 55 moves the tap of pitch command potentiometer $3 inthe appropriate direction. thus unbalancing the bridge network. andimpressing a pitch change signal on the series connected controlwindings of amplifiers 59 and 60. Pitch servo motor 51 is responsive toamplifier 60 through differential relay 6i to obtain very sensitivepitch control. Servo motor 51 rotates gear 50. which in turn causes apivotal deflection of differential lever 47 about point 49. stroking thespool of pilot valve 43. Pilot valve 43 in turn hydraulically strokesservo valve 44 to direct power fluid to piston 24 so as to change thepitch in the commanded sense. Because of the connection between theported sleeve of the pilot valve and the spool of servo valve 44. theservo valve spool follows exactly the movement of the pilot valve spool.As, the pitch changes. piston rod 25 moves. thus rotating differentiallever 47 about its connection to rod 48. and returning the pilot valvespool to its normal closed position. The pilot valve in turnhydraulically strokes the spool of servo valve 44 to return it to itsnormal closed position. Thus. the propeller pitch is at the commandedangle. and is held in this position until the control handle is moved toa further position. The bridge of the command circuit is. of course.already ugsin balanced by virtue of the followup movement ofpotentiometer 52 by servo motor 51 and gear 50.

The hydraulic oil supply is normally from low volume. constantdeliverypump 34, which obtains a low rate of pitch change. This low rateminimizes the detrimental effect of inertia and time constantsthroughout the servo loop. and thus very precise pitch positioning isobtained. High volume pump 33 normally discharges to sump throughunloading valve 41. When large pitch changes at a rapid rate aredemanded to facilitate maneuvering. unloading valve 41 is closed bysolenoid valve 42, thus causing the high volume output of pump 33 tocombine with that of pump 34. An additional advantage in unloading thehigh volume pump is the saving in power loss caused by servo valvepressure drop. The solenoid of venting valve 42 is energized byamplifier 59 through relay 62 whenever pitch command leads the actualpitch by 5". Likewise. the solenoid is de-energized when this lead angleis reduced to less than S". The signal level. of course. rises inproportion to the lead angle or servo error. The high volume pump is cutin and cut out at a predetermined lead angle by suitable amplified gainadjustment.

As mentioned previously, governor 67 is capable of measuring engineoverload. and of rotating rhcostat 66 in proportion to the magnitudeofthe overload. By connecting rhcostat 66 in series with one side ofcommand potentiometer 53. pitch will automatically be reduced to relievethe engine overload. since the rhcostat will automatically bias thecommand circuit in a pitch reducing sense. With the rhcostat 66cohnected in the command circuit as illustrated in FIG. 38. it would beeffective to reduce pitch in only one mode of-operation. for instance.when the propeller is in an ahead pitch condition. To render iteffective during astcrn pitch operation. it should be electricallyrelocated so as to be in series connection with the over side of commandpotentiometer 53. in the iilustratcd embodiment. this is accomplishedautomatically by providing an additional cam 56 which is driven bycontrol handle 54. and is effective upon movement of the control handleto. for instance. an astern pitch position to automatically close switch65. thus energizing solenoid 64 and its associated relay contacts 63 torelocate rhcostat 66 electrically on the opposite side ofcommandpotentiometer 53. v

The details of the improved and preferred pilot valve and servo valvearrangement are shown in FIG. 5. As shown in FIG. 5. the servo valvespool has lands 78 and 79 which are effective to direct power fluid frominlet 73 to one or the other of ports 76 and 77. while venting one ofthese ports to sump through vent connections 74 and 75. The servo valvespool is hydraulically stroked by the admission of pressure fluid tospace 81 through port or to space 82 through port 86 under the controlof the pilot valve. The spool of the pilot valve is mechanically strokedby the connecting member indicated schematically at 46. Sleeve 45 of thepilot valve is mechani cally connected to the spool ofthe servo valve bybolts or the like. one of which is shown at 92. Pilot fluid forstrokingthe servo valve spool is supplied to the pilot valve at inlet port 7 l.and passes through port 83 in sleeve 45 to an annular space 84 which isboundaried at its ends by lands 85 and 87 of the pilot spool. Lands 85and 87 control ports 86 and 88. respectively. in sleeve 45.- Ports 89and 90 in pilot spool 93 communicate with an interior venting passage 72which discharges to sump. When assembled. the passage 94 is connectedwith port 80 of space 81.

in operation. when pilot spool 93 is stroked by connection 46 to theleft as viewed in FIG. 5. land 85 moves to the left, opening port 86 insleeve 45. and admitting pilot fluid from annular space 84 to the space82. At thesame time. land 87 moves to the left. covering port 88. andopening space 81 of the servo valve spool to sump through port 80. aconnecting conduit to passage 94. ports 88 and 90. and discharge passage72. Thus the servo valve spool is hydraulically stroked to the left asviewed in FIG. 5. As the servo spool and hence ported sleeve 45 move tothe left. ports 86 and 88 are closed by the movement of the sleeve 45.and hence the servo spool follows precisely the initial movement of thepilot spool 93. and is held in the new position corresponding to thestroked position of g the pilot spool.

When the pilot spool 93 is returned to the right through the action ofthe differential lever arrangement. space 82 is connectedtosump'.'and'space 81 is connected to the pilot fluid. thushydraulieallystroking the-servo spool to the right. and stopping it at a new"position corresponding exactly to the new position of the pilot spool93.

I From the foregoing description of exemplary embodiments. it isbelieved that the arrangement, operation and advantages of the basicvariable rate actuator system will be easily understood by personsskilled in the art. as will the arrangements. operation and advantagesof the particular improved steering system and the pitch and speedcontrol system with their additional improved features.

The various components of the illustrated systems are eithercommercially available or easily fabricated. For instance. load sensinggovernor 67 is of a well known design manufactured by Woodward GovernorCompany, and designated as Model lG-PL. Unloading valves l7 and 41 canconveniently be of the type illustrated in Kent's Mechanical EngineersHandbook. l2th Edition. Design and Production. pp. l3- l6. H6. 32. Theprogrammed pitch and speed control cams are easily fabricated and shapedappropriately for the program desired in a particular system. in thisrespect. it is to be noted that in actual practice the cams preferablyare not mechanically connected directly to the control lever. but aredriven by a servo loop which in turn is controlled by the control lever.The servo loop controls the rate of rotation of the cams so as to avoidthe possibility of. for instance. the speed change departing from itsprogrammed relationship with the pitch change. Thus. in the event of ahard-over signal from full astern to full ahead. the engine speed mightbe brought back to full before the pitch actuator could complete thepitch change. if the rate of rotation ofthe cams were not controlled. Byusing a servo loop. the cams can be moved just fast enough to maintain.for instance. a l pitch error. This would keep the hydraulic system athigh capacity. but would not allow the cams to run away from the pitchservo.

it will be readily apparent to those skilled in the art that theexemplary preferred embodiments described and illustrated herein aresusceptible of various modifications. rearrangements. etc.. withoutdeparting from the spirit and substance of the invention. Accordingly.it is to be understood that the disclosed embodiments are illustrativerather than limiting. and that the scope of the invention is as setforth in the appended claims construed in the light of the foregoingdescriptions and illustrations.

We claim:

I. A variable rate electrohydraulic actuator system comprising ahydraulic motor. a motor control electric circuit for carrying avariable motor command signal indicative of a commanded operation ofsaid motor. first and second hydraulic pumps. first pump control means.including amplifier means. operatively associated with said electriccircuit and responsive to said command signal for directing power fluidfrom said first pump to said motor in response to a command signalindlcative of commanded operation of a relatively low magnltude. andsecond pump control means. including amplifier means. operativelyassociated with said electric circuit and continuously subjected to saidcommand signal. but relatively less sensitive thereto than said firstpump control means. for directing power fluid from said second pump tosaid motor only in response to and during a predetermined command signalindicative of a commanded operation of a relatively greater magnitudeand only when the output of said first pump is directed to said motor.said second pump control means being substantially insensitive to saidcommand signal indicative of a commanded operation of a relatively lowmagnitude.

2. A system as claimed in claim 1 wherein said first and second pumpsare constant delivery pumps. and said first and second pump controlmeans include means for bypassing the power fluid from each respectivepump when the power fluid from that pump is not directed to said motor.

3. A system as claimed in claim 2 wherein said motor control circuitincludes operator actuated motor command means. and means for generatinga command signal in response to a relative difference between acommanded motor condition and the actual motor condition.

4. A system as claimed in claim 3 wherein said means for generating acommand signal comprises a command potentiometer operatively coupled tosaid operator actuated motor command means and a feedback-followuppotentiometer operatively coupled to said hydraulic motor.

5. A system as claimed in claim 1 wherein said first and second pumpcontrol means respectively include magnetic amplifiers of differentoutput sensitivities.

6. A system as claimed in claim 5 wherein said magnetic amplifiers havetheir inputs connected in series in said motor control electric circuit.

7. A system as claimed in claim l wherein said electric circuit carriesa variable motor command signal indicative of a commanded direction andmagnitude of operation ofsaid motor. and said first pump control meansincludes a selector valve for directing power fluid to said motor so asto operate the motor in the commanded direction.

8. A system as claimed in claim 1 wherein said hydraulic motor comprisesa hydraulic rudder actuator operatively coupled to the rudder ofa marinevessel. and wherein said electric circuit includes means operativelycoupled to the steering control and to the rudder for establishing a netcommand signal the polarity of which is indicative of the commandeddirection of rudder movement and the magnitude of which is indicativeofthe commanded extent of rudder movement; and wherein said first pumpcontrol means includes a selector valve for bypassing the output of saidfirst pump or connecting the output to one side or the other of saidrudder actuator. a magnetic amplifier connected in said circuit. and adifferential relay controlled by said magnetic amplifier for actuatingsaid selector valve. said magnetic amplifier and said differential relayin combination being relatively sensitive to the net command signal insaid circuit; and wherein said second pump control means comprises valvemeans for bypassing the output of said second pump or combining it withthe output of said first pump. a magnetic amplifier connected in saidcircuit. and a relay controlled by the last mentioned amplifier foractuating said last mentioned valve. said last mentioned amplifier andrelay in combination being relatively insensitive to the net commandsignal in said circuit so as to combine theoutput of said second pumpwith said first pump only when the net command signal is indicative of arelative large extent of commanded rudder movement.

9. A system as claimed in claim 8 wherein said two magnetic amplifiershave their inputs connected in series in said circuit.

10. A system as claimed in claim 1 wherein said hydraulic motorcomprises a pitch changing actuator operatively coupled to the pitchchanging linkage ofa variable pitch propeller of a marine vessel; andwherein said electric circuit includes means operatively coupled to apitch control member and to the actuator for establishing a net commandsignal the polarity of which is indicative of the commanded sense ofpitch change and the magnitude of which is indicative of the extent ofpitch change; and wherein said first pump control means includes aselector valve for bypassing the output of said first pump or directingthe output to one side or the other of said actuator. a magneticamplifier connected in said circuit. and a differential relay controlledby said magnetic amplifier for actuating said selector valve, saidmagnetic amplifier and said differential relay in combination beingrelatively sensitive to the net command signal in said circuit; andwherein said second pump control means includes valve means forbypassing the output of said second pump or combining it with the outputof said first pump. a magnetic amplifier connected in said circuit. anda relay controlled by said last mentioned amplifier for actuating saidlast mentioned valve. said last mentioned amplifier and relay incombination being relatively insensitive to the net command signal insaid circuit so as to combine the output of said second pump with saidfirst pump only when the net command signal is indicative of arelatively large extent of commanded pitch change.

11. A variable rate electrohydraulic actuator system for use inactuating a control member ofa marine vessel, comprising a hydraulicmotor. first and second constant delivery pumps. a common signal sourcefor establishing a variable motor command electrical signal, and meansoperatively connected to said common signal-source but selectivelyresponsive to said variable motor command signal for selectivelydirecting the output of one or both or neither of said pumps to saidhydraulic motor. depending upon the particular command signalestablished by said common signal source. thereby to operate said motorselectively at variable rates, said means operatively connected to saidcommon signal source including two amplifiers in circuit with saidcommon signal source, one for con trolling each pump, and amplifierresponsive means operatively combined with each amplifier forselectively directing the output of the associated pump to said motor orto bypass. one of said amplifiers and its amplifier responsive meansbeing sensitive to said variable control signal of a certain range. andthe other of said amplifiers and its amplifier responsive means beingsensitive to said variable control signal only in a portion of saidrange different from the portion to which said one amplifier isinitially responsive.

12. A systemas claimed in claim ll wherein said amplifiers have theirinputs series connected in circuit with said common signal source.

13. A system as claimed in claim 12 wherein said common signal sourcecomprises motor position command means and motor position sensing meansfor establishing a motor command electrical signal indicative of thedifference between the commanded position and the sensed position, andwherein said other amplifier and its amplifier responsive means aresensitive only to signals indicative of a relatively large differertce.

l4. A system as claimed in claim l3 wherein said motor position commandmeans and said motor position sensing means comprise potentiometers.each of which forms two arms of a d.c. bridge network. and the taps ofwhich are series connected. said amplifiers being located in the seriesconnection between said taps.

15. A system as claimed in claim 14 wherein one of said amplifierresponsive means comprises a differential relay and a selector valve fordirecting the output of said pumps to one side or the other of saidmotor in response to the polarity of the variable electric signal.

16. A system as claimed in claim ll wherein said hydraulic motor is apropeller pitch actuator operatively coupled to a variable pitchpropeller for a marine vessel. and wherein said common signal sourcecomprises a circuit including pitch command means and pitch sensingmeans for establishing a pitch changing electrical signal indicative ofthe difference between the commanded pitch and the sensed pitch. furthercomprising means adapted to be operatively coupled to a propulsionengine for sensing the load condition thereon and biassing the circuitin the pitch reducing sense in response to an overload condition.

17. A system as claimed in claim 16 wherein said pitch command means andsaid pitch sensing means comprise two potentiometer: in a bridgearrangement in said circuit. each potentiometer forming two arms of thebridge and the taps of the potentiometers being series connected, andsaid means for biassing said circuit comprises a rheostat. and saidmeans operatively connected to said signal source is responsive also tothe polarity of said variable motor command signal so as to direct theselected pump output to the motor for driving it in the pitch increasingor decreasing direction for either ahead or astern propulsion. furthercomprising means for connecting said rheostat in said bridge atdifferent electrical locations so that it will bias the circuit in apitch reducing sense in response to an engine overload conditionregardless of whether the propeller has astern or ahead pitch.

[8. A system as claimed in claim 17 wherein said pitch commandpotentiometer is operatively coupled to a control member having aheadand astern positions, and said means for connecting said rheostat insaid bridge comprises switch means for changing the electrical locationof said rheostat in response to movement of said control member fromeither of said positions to the other.

l9. A system as claimed in claim l7 wherein said rheostat is selectivelyseries connected in one or the other of the two arms formed by one ofsaid potentiometers.

20. A system as claimed in claim ll wherein said means for selectivelydirecting the output of said pumps includes a compound distributor valvemeans. said valve means comprising a main servo valve having a movablemember for selectively connecting the output to one side or the other ofsaid motor so as to drive the motor in a given direction, a pilot valvehaving a movable member for directing actuating fluid selectively tosaid servo valve to move said movable member of said servo valve so asin turn to direct the output to the selected side of the hydraulicmotor. and means for stopping the movement of said movable member ofsaid servo valve when it has moved a distance corresponding to themovement of the movable member of said pilot valve.

21. A system as claimed in claim 20 wherein said movable member of saidservo valve comprises a servo spool, and said servo spool isreciprocable in a ported servo valve body in response to actuating fluiddirected selectively to the ends of said servo spool by said pilotvalve. and wherein said movable member of said pilot valve comprises apilot spool. and said pilot spool is reciprocable in a ported sleeve inresponse to said motor command signals, said ports in said sleeve beingin communication with the ends of said servo spool so as to directactuating fluid thereto and therefrom when opened by said pilot spool.and wherein said means for stopping the movement of said servo spoolcomprises means coupling said servo spool to said ported sleeve forcommon movement. whereby a port in said sleeve which is opened bymovement of said pilot spool will be closed upon the resultingcorresponding movement of said servo spool and said sleeve.

22. A variable rate electrohydraulic actuator system for use inactuating a control member of a marine vessel. comprising a hydraulicmotor. first and second constant delivery pumps. a common signal sourcefor establishing a variable motor command electrical signal. and meansoperatively connected to said common signal source but selectivelyresponsive to said variable motor command signal for selectivelydirecting the output of one or both or neither or said pumps to saidhydraulic motor. depending upon the particular command signalestablished by said common signal source, thereby to operate said motorselectively at variable rates. said means operatively connected to saidcommon signal source including amplifier means having two outputs ofdifferent output sensitivities.

